Grip Force Variability Research Articles

Grip Force on Steering Wheel as a Measure of Stress.

Driver performance is crucial for road safety. There is a relationship between performance and stress such that too high or too low stress levels (usually characterized by stressful or careless driving, respectively) impair driving quality. Therefore, monitoring stress levels can improve the overall performance of drivers by providing either an alert or intervention when stress levels are sub-optimal. Commonly used stress measures suffer from several shortcomings, such as time delays in indication and invasiveness of sensors. Grip force is a relatively new measure that shows promising results in measuring stress during psychomotor tasks. In driving, grip force sensor is non-invasive and transparent to the end user as drivers must continuously grip the steering wheel. The aim of the current research is to examine whether grip force can be used as a useful measure of stress in driving tasks. Twenty-one participants took part in a field experiment in which they were required to brake the vehicle in various intensities. The effects of the braking intensity on grip force, heart rate, and heart rate variability were analyzed. The results indicate a significant correlation between these three parameters. These results provide initial evidence that grip force can be used to measure stress in driving tasks. These findings may have several applications in the field of stress and driving research as well as in the vehicle safety domain.

Longitudinal Assessment and Functional Neuroimaging of Movement Variability Reveal Novel Insights Into Motor Dysfunction in Clinical High Risk for Psychosis.

Motor dysfunction in youth at clinical high risk (CHR) for psychosis is thought to reflect abnormal neurodevelopment within cortical-subcortical motor circuits and may be important for understanding clinical trajectories of CHR individuals. However, to date, our perspective of brain-behavior relationships has been informed solely by cross-sectional correlational studies linking behavior in the lab to brain structure or respective resting-state network connectivity. Here, we assess movement dysfunction from 2 perspectives: study 1 investigates the longitudinal progression of handwriting variability and positive symptoms in a sample of 91 CHR and healthy controls during a 12-month follow-up and study 2 involves a multiband functional magnetic resonance imaging task exploring the relationship between power grip force stability and motor network brain activation in a subset of participants. In study 1, we found that greater handwriting variability was a stable feature of CHR participants who experienced worse symptom progression. Study 2 results showed that CHR individuals had greater variability in their grip force and greater variability was related to decreased activation in the associative cortico-striatal network compared to controls. Motor variability may be a stable marker of vulnerability for psychosis risk and possible indicator of a vulnerable cortico-striatal brain network functioning in CHR participants, although the effects of antipsychotic medication should be considered.

Impaired force control contributes to car steering dysfunction in chronic stroke

Purpose Precise control of a car steering wheel requires adequate motor capability. Deficits in grip strength and force control after stroke could influence the ability steer a car. Our study aimed to determine the impact of stroke on car steering and identify the relative contribution of grip strength and grip force control to steering performance. Methods Twelve chronic stroke survivors and 12 controls performed three gripping tasks with each hand: maximum voluntary contraction, dynamic force tracking, and steering a car on a winding road in a simulated driving environment. We quantified grip strength, grip force variability, and deviation of the car from the center of the lane. Results The paretic hand exhibited reduced grip strength, increased grip force variability, and increased lane deviation compared with the non-dominant hand in controls. Grip force variability, but not grip strength, significantly predicted (R 2 = 0.49, p < 0.05) lane deviation with the paretic hand. Conclusion Stroke impairs the steering ability of the paretic hand. Although grip strength and force control of the paretic hand are diminished after stroke, only grip force control predicts steering accuracy. Deficits in grip force control after stroke contribute to functional limitations in performing skilled tasks with the paretic hand. Implications for rehabilitation Driving is an important goal for independent mobility after stroke that requires motor capability to manipulate hand and foot controls. Two prominent stroke-related motor impairments that may impact precise car steering are reduced grip strength and grip force control. In individuals with mild-moderate impairments, deficits in grip force modulation rather than grip strength contribute to compromised steering performance with the paretic hand. We recommend that driving rehabilitation should consider re-educating grip force modulation for successful driving outcomes post stroke.

External biomechanical constraints impair maximal voluntary grip force stability post-stroke

BackgroundGrip strength is frequently measured as a global indicator of motor function. In clinical populations, such as hemiparesis post-stroke, grip strength is associated with upper-extremity motor impairment, function, and ability to execute activities of daily living. However, biomechanical configuration of the distal arm and hand may influence the magnitude and stability of maximal voluntary grip force and varies across studies. The influence of distal arm/hand biomechanical configuration on grip force remains unclear. Here we investigated how biomechanical configuration of the distal arm/hand influence the magnitude and trial-to-trial variability of maximal grip force performed in similar positions with variations in external constraint. MethodsWe studied three groups of 20 individuals: healthy young, healthy older, and individuals post-stroke. We tested maximal voluntary grip force in 4 conditions: 1: self-determined/“free”; 2: standard; 3: fixed arm-rest; 4: gripper fixed to arm-rest, using an instrumented grip dynamometer in both dominant/non-dominant and non-paretic/paretic hands. FindingsRegardless of hand or group, maximal voluntary grip force was highest when the distal limb was most constrained (i.e., Condition 4), followed by the least constrained (i.e., Condition 1) (Cohen's f = 0.52, P's < 0.001). Coefficient of variation among three trials was greater in the paretic hand compared with healthy individuals, particularly in more (Conditions 3 and 4) compared to less (Conditions 1 and 2) constrained conditions (Cohen's f = 0.29, P's < 0.05). InterpretationThese findings have important implications for design of rehabilitation interventions and devices. Particularly in individuals post-stroke, external biomechanical constraints increase maximal voluntary grip force variability while fewer biomechanical constraints yield more stable performance.

Control of Precision Grip Force in Lifting and Holding of Low-Mass Objects.

Few studies have investigated the control of grip force when manipulating an object with an extremely small mass using a precision grip, although some related information has been provided by studies conducted in an unusual microgravity environment. Grip-load force coordination was examined while healthy adults (N = 17) held a moveable instrumented apparatus with its mass changed between 6 g and 200 g in 14 steps, with its grip surface set as either sandpaper or rayon. Additional measurements of grip-force-dependent finger-surface contact area and finger skin indentation, as well as a test of weight discrimination, were also performed. For each surface condition, the static grip force was modulated in parallel with load force while holding the object of a mass above 30 g. For objects with mass smaller than 30 g, on the other hand, the parallel relationship was changed, resulting in a progressive increase in grip-to-load force (GF/LF) ratio. The rayon had a higher GF/LF force ratio across all mass levels. The proportion of safety margin in the static grip force and normalized moment-to-moment variability of the static grip force were also elevated towards the lower end of the object mass for both surfaces. These findings indicate that the strategy of grip force control for holding objects with an extremely small mass differs from that with a mass above 30 g. The data for the contact area, skin indentation, and weight discrimination suggest that a decreased level of cutaneous feedback signals from the finger pads could have played some role in a cost function in efficient grip force control with low-mass objects. The elevated grip force variability associated with signal-dependent and internal noises, and anticipated inertial force on the held object due to acceleration of the arm and hand, could also have contributed to the cost function.

Effects of transcranial direct current stimulation in combination with motor practice on dexterous grasping and manipulation in healthy older adults

Transcranial anodal stimulation (tDCS) over primary motor cortex (M1) improves dexterous manipulation in healthy older adults. However, the beneficial effects of anodal tDCS in combination with motor practice on natural and clinically relevant functional manual tasks, and the associated changes in the digit contact forces are not known. To this end, we studied the effects of 20 min of tDCS applied over M1 for the dominant hand combined with motor practice (MP) in a sham‐controlled crossover study. We monitored the forces applied to an object that healthy elderly individuals grasped and manipulated, and their performances on the Grooved Pegboard Test and the Key‐slot task. Practice improved performance on the Pegboard test, and anodal tDCS + MP improved retention of this performance gain when tested 35 min later, whereas similar performance gains degraded in the sham group after 35 min. Interestingly, grip force variability on an isometric precision grip task performed with visual feedback of precision force increased following anodal tDCS + MP, but not sham tDCS + MP. This finding suggests that anodal tDCS over M1 might alter the descending drive to spinal motor neurons involved in the performance of isometric precision grip task under visual feedback leading to increased fluctuations in the grip force exerted on the object. Our results demonstrate that anodal stimulation in combination with motor practice helps older adults to retain their improved performance on a functionally relevant manual task in healthy older adults.

Grasping multiple sclerosis: do quantitative motor assessments provide a link between structure and function?

Motor disability in MS is commonly assessed by the Expanded Disability Status Scale (EDSS). Categorical rating scales are limited by subjective error and inter-rater variability. Therefore, objective and quantitative measures of motor disability may be useful to supplement the EDSS in the setting of clinical trials. It was previously shown that grip-force-variability (GFV) is increased in MS. We hypothesized that GFV may be an objective measure of motor disability in MS. To investigate whether the increase in GFV in MS is correlated to the clinical disability as assessed by the EDSS and to microstructural changes in the brain as assessed by diffusion tensor imaging, GFV was recorded in a grasping and lifting task in 27 MS patients and 23 controls using a grip-device equipped with a force transducer. The EDSS was assessed by neurologists experienced in MS. Patients underwent diffusion tensor imaging at 3T to assess the fractional anisotropy (FA) of the cerebral white matter as a measure of microstructural brain integrity. GFV was increased in MS and correlated to changes in the FA of white matter in the vicinity of the somatosensory and visual cortex. GFV also correlated with the EDSS. GFV may be a useful objective measure of motor dysfunction in MS linked to disability and structural changes in the brain. Our data suggests that GFV should be further explored as an objective measure of motor dysfunction in MS. It could supplement the EDSS, e.g., in proof of concept studies.

Grip Force Variability and Its Effects on Children’s Handwriting Legibility, Form, and Strokes

A comprehensive understanding of the underlying biomechanical processes during handwriting is needed to accurately guide clinical interventions. To date, quantitative measurement of such biomechanical processes has largely excluded measurements of the forces exerted radially on the barrel of the writing utensil (grip forces) and how they vary over time during a handwriting task. An instrumented writing utensil was deployed for a direct measurement of kinematic and temporal information during a writing task, as well as forces exerted on the writing surface and on the barrel of the pen. The writing utensil was used by a cohort of 35 students (19 males), 16 in first grade and 19 in second grade, as they performed the Minnesota Handwriting Assessment (MHA) test. Quantitative grip force variability measures were computed and tested as correlates of handwriting legibility, form, and strokes. Grip force variability was shown to correlate strongly with handwriting quality, in particular for students classified by the MHA as nonproficient writers. More specifically, static grip force patterns were shown to result in poor handwriting quality and in greater variation in handwriting stroke durations. Grip force variability throughout the writing task was shown to be significantly lower for nonproficient writers (t-test, p<0.01) while the number of strokes and per-stroke durations were shown to be higher (p<0.03). The results suggest that grip force dynamics play a key role in determining handwriting quality and stroke characteristics. In particular, students with writing difficulties exhibited more static grip force patterns, lower legibility and form scores, as well as increased variation in stroke durations. These findings shed light on the underlying processes of handwriting and grip force modulation and may help to improve intervention planning.

Grasping premanifest Huntington's disease – shaping new endpoints for new trials

Future clinical trials in subjects with premanifest Huntington's disease (preHD) may depend on the availability of biomarkers. It was previously shown in symptomatic HD that, the grip force variability coefficient-of-variation (GFV-C) in a grasping paradigm was correlated to the Unified-Huntington's-Disease-Rating-Scale-Total-Motor-Score (UHDRS-TMS) and increased in a 3 year follow-up study. To further elucidate its potential as a biomarker, we investigated whether GFV-C is able to detect a motor phenotype in preHD and is correlated to the genotype assessed by a disease-burden-score. The ability of preHD (n = 15) and symptomatic HD subjects (n = 20) to maintain stable grip forces, while holding an object (250 g and 500 g), was measured and compared with the controls (n = 19). GFV-C was increased in preHD at 500 g, in symptomatic subjects at both weights and was correlated to the disease-burden-score and UHDRS-TMS. GFV-C may be a useful objective and quantitative marker of motor dysfunction across genetically diagnosed premanifest and symptomatic HD subjects.

Objective motor phenotype assessment in multiple sclerosis: deficits in grip force coordination correlate to changes in diffusion tensor imaging

Background: Complex motor deficits are common symptoms in patients with Multiple Sclerosis (MS). Objective and quantitative measures of motor phenotype may increase the sensitivity of clinical trials. We previously found increased grip force variability in patients with MS and correlation of deficits in grip force variability to the EDSS. Diffusion Tensor Imaging (DTI) and analysis of fractional anisotropy (FA) are reliable methods to investigate microstructural damage of the white matter tissue in MS.

Grip-force variability in asymptomatic carriers of the Huntington gene – a biomarker for presymptomatic clinical studies?

Aims: Isometric grip force variability (GFV) in Huntington's Disease (HD) was shown to correlate with (1) the severity of motor deficits in HD as assessed in the UHDRS (Gordon et al. 2000), (2) the CAG-repeat length when normalized for age (Reilmann et al. 2004), and (3) the degree of atrophy observed in the caudate nucleus on MRI volumetry (Reilmann et al 2005). Furthermore grip force variability was shown to increase in the course of HD (Reilmann et al. 2001). Objective: To investigate whether GFV in a grasping and holding task is pathologically increased in clinically asymptomatic carriers of the Huntington gene. Subjects and methods: HD gene carriers (n=13) and age-and-sex-matched healthy controls (n=13) were instructed to grasp and lift an object (weight 250g or 500g) in the precision grip and hold it next to a marker 10cm high for 30 seconds. Thirteen trials were performed in each weight condition. Grip and lift forces were recorded using force transducers (Mini-30, ATI, USA). Object position was recorded using a 3D-tracking device (Fastrack, Polhemus, USA). Data was recorded and analyzed using a flexible laboratory computer system (SC/ZOOM, University of Umea, Sweden). Mean grip force and its coefficient of variation were calculated during a 20s period in the static holding phase. Gene carriers were clinically assessed by the UHDRS and exhibited total motor scores <4, i.e. presymptomatic stage. Statistics were performed using ANOVA (SPSS 13.0). Results: Grip force variability in the static holding phase was increased in HD gene carriers compared to healthy controls in the 250g object condition (p<0.05). The difference in the 500g object condition did not reach statistical significance (p=0.07). Conclusion: Assessment of isometric grip forces may enable investigators to detect and objectively quantify impairments in motor dysfunction in subjects prior to clinical manifestation of HD. Similar to symptomatic HD patients, impairments in grip force control are more evident in the lighter object condition (see Gordon et al. 2000, Fellows et al. 1997). A possible use of GFV as a surrogate marker in neuroprotective treatment trials in asymptomatic HD gene carriers warrants further exploration, e.g. in a blinded follow-up study. Acknowledgment: The study was supported by grant IMF-RE-120225 from the “Innovative Medizinische Forschung“, Faculty of Medicine, University of Munster to RR

Altered isometric force control during object release in patients with Huntington's Disease

Background: Objective markers for the severity of motor dysfunction are warranted for clinical trials in patients with Huntington's Disease (HD). Specific impairments in the control of isometric grip forces were found in grasping, holding, and transport tasks in HD. In previous studies we identified „grip force variability“ (GFV) as a measure correlated (1) to the clinical severity of the disease as assessed in the UHDRS, (2) to the amount of neurodegeneration in MRI volumetry, and (3) to the CAG repeat length when corrected for the age of patients. Thus GFV may be a surrogate marker to objectively assess the severity of HD. While the initiation and maintenance of grip forces in grasping and lifting has intensively been investigated in HD, it is unknown if specific impairments occur during object release in HD.

Children's coordination of force output in a pinch grip task

This study examined the role of sensorimotor system noise in the organization of the force output of the thumb and index finger and the coordination between the two digits in an isometric pinch grip force task as a function of age (6, 8, 10, 18-22 years), feedback condition (with and without visual feedback information), and force level (5, 15, 25, and 35% of maximal voluntary force. With increases in age under the visual feedback conditions, the signal-to-noise ratio increased, the sequential structure of the force output signals became more irregular, the degree of coherence between the digits at higher force levels was enhanced, and the digits exhibited a greater degree of coherence across the higher frequencies of the power spectrum at all force levels. However, these age differences were either minimized or eliminated under conditions without feedback. These findings show that the age-related performance differences in grip force variability are primarily due to more effective use of visual information rather than age differences in intrinsic sensorimotor noise.

Objective assessment of progression in Huntington's disease: a 3-year follow-up study.

Objective measures to assess progression of Huntington's disease (HD) are desirable. The authors have previously found that patients with HD with higher Unified Huntington's Disease Rating Scale (UHDRS) motor scores exhibited higher variability of isometric grip forces while grasping an object. Therefore, the authors assessed grip force variability during this task in 10 HD patients with a 3-year follow-up. Grip force variability increased in all patients at the follow-up. Thus, grip force variability during grasping might be an objective and quantitative measure to assess motor deficits associated with the progression of HD.